Referenced-applications
The present application claims the priority of Japanese Patent Application No. 11-72640, filed on Mar. 17, 1999, the entire contents of which are hereby incorporated herein by reference.
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1. Description of Related Art
Conventionally, the chief method employed for growing titanium nitride thin film on a substrate such as for a semiconductor device, electronic components of various types, or sensors of various types was reactive sputtering, using a metallic titanium target and nitrogen gas. In recent years, with ultra-miniaturization of large-scale silicon integrated circuits, the design rule of DRAMs of 64 megabits or more has become less than 0.35 xcexcm, approximately, and, furthermore, the aspect ratio of device contact holes is increasing. When titanium nitride thin film is employed as the barrier metal of such contact holes, if the titanium nitride thin film is deposited by the conventional reactive sputtering method, there is the problem that step coverage is poor. In particular, conformal deposition on the side walls cannot be achieved. If the step coverage is poor, the electrical characteristics of the semiconductor device are adversely affected. It is anticipated that this may present serious problems in manufacture of next-generation devices. Deposition of a conformal barrier metal using the CVD method, having excellent contact hole filling characteristics and coverage characteristics is therefore desired.
Against this background, techniques for manufacturing titanium nitride thin films by the CVD method (chemical vapor-phase deposition method) have therefore attracted attention in recent years. Various CVD methods and/or source-material gases for manufacture of titanium nitride thin films are currently being proposed, and one of these is a technique using tetrakisdialkylamino titanium (herein below abbreviated to TDAAT), which is an organo-metallic compound. The chemical structural formula of this TDAAT is shown in FIG. 5. In this chemical structural formula, R is an alkyl group. When this R is an ethyl group, the compound is tetrakisdiethylamino titanium (abbreviated hereinbelow to TDEAT).
These organo-titanium compounds are liquid at room temperature and atmospheric pressure, but are supplied in vaporized form into the reaction vessel through a shower head together with carrier gas such as H2, Ar, or N2. An added gas (ammonia gas) that reacts chemically with the organo-titanium compound is also supplied into the reaction vessel. A substrate is present in the reaction vessel, this substrate being maintained at a prescribed reaction temperature.
The organo-titanium compound and added gas generate a reaction that produces titanium nitride, with the result that a film of titanium nitride (TiN) is deposited on the substrate. It is known that the electrical properties and step coverage of the titanium nitride that is deposited depend on the flow rate of the organo-titanium compound and added gas that react within the reaction vessel and on the substrate temperature and reaction pressure.
For example, in Ivo J. Raajimakers, xe2x80x9cLow temperature MOCVD of advanced barrier layersxe2x80x9d, Thin solid films, 247 (1994) 85-93, or reference literature cited therein, titanium nitride thin film is manufactured by supplying source material TDAAT together with a carrier gas into a reaction vessel, further employing ammonia gas (NH3) as added gas. The flow rate of the ammonia gas is 1000 sccm, or more. When the titanium nitride thin film that was obtained was deposited on contact holes of diameter 0.8 xcexcm and an aspect ratio of 1, good step coverage of 85% was obtained. However, in the case of the contact holes of diameter of 0.35 xcexcm or less that are employed in 64 megabit DRAMs, it is anticipated that the step coverage would be less than 20%.
Also, Jackson et al xe2x80x9cR. L. Jackson, E. J. M Cineney, B. Roberts, J. Strupp, A. Velaga, S. Patel, and L. Halliday, Proc. Advanced Metallization for ULSI Application, ed. by D. P. Favreau, Y. Shacham-Diamond, and Y. Horiike (Mat. Res. Soc., Pittsburgh, Pa., 1994), p. 20xe2x80x9d vaporized TDEAT source material by passing it through a vaporizer, and supplied this to a reaction vessel through a shower head together with nitrogen gas as a carrier gas. Titanium nitride thin film was manufactured by further adding ammonia gas (NH3) by passing this through a shower head on a separate path. This reference reports in particular the effect of the ratio of the amounts of source material and ammonia gas supplied. In the case of contact holes of diameter 0.35 xcexcm and an aspect ratio of 3.4, under the conditions: deposition temperature 350xc2x0 C., pressure 10 to 50 Torr, the step coverage decreased from 65% to about 20% with an increase in the amount of ammonia gas added. Further, when the deposition temperature was raised to 425xc2x0 C., for the same contact holes, the step coverage fell to 5%. Thus, in the case of TDEAT, when the flow rate of ammonia gas was increased, insufficient step coverage of fine contact holes was obtained.
Accordingly, the inventors proposed, in Japanese patent application number 10-241138, filed on Aug. 13, 1998, a method of manufacturing a thin film and a thin-film manufacturing device that makes possible the deposition of an excellent TiN film of step coverage of better than 70% of contact holes of an aspect ratio of 4, by specifying the respective flow rates and flow speeds of TDAAT and its carrier gas (N2) and the added ammonia gas and its carrier gas (N2). However, at the stage of the previous application, excellent film deposition with step coverage better than 70% in respect of holes of aperture diameter of 0.25 xcexcm or less and an aspect ratio of 6 or more was difficult.
In the prior art of Jackson et al, referred to above, it was established that step coverage of contact holes was adversely affected when ammonia gas was added to TDAAT. This presented a considerable problem in the adoption of the technique of deposition of titanium nitride by the CVD method using an organic titanium compound in the mass-production of semiconductor devices.
However, while it was established by the previous application of the present inventors, mentioned above, that excellent step coverage of holes having an aspect ratio of 4 could be obtained by trace addition of ammonia gas, the problem remained that this was difficult in practice in respect of holes of an aspect ratio of 6 or more.
2. Field of the Invention
This invention relates to a method and device for manufacturing titanium nitride thin film by supplying TDAAT gas and ammonia gas into a reaction vessel, the gas pressure and temperature being controlled with the object of obtaining excellent step coverage in regard to holes of aspect ratio 6 or more, using the CVD method.
This invention relates to a method of manufacturing titanium nitride thin film and a manufacturing device therefor, using TDAAT as source material, by optimizing the rate of supply (partial pressure) of added ammonia gas when titanium nitride thin film is manufactured by the CVD method, with an object of obtaining excellent step coverage of contact holes or grooves having an aperture diameter of under 0.25 xcexcm and an aspect ratio of more than 6.
A method of manufacturing a titanium nitride thin film according to this invention includes the deposition of a titanium nitride thin film onto a substrate by the CVD method using tetrakisdialkylamino titanium (TDAAT) and ammonia gas that reacts therewith, whose chief characteristic is that the range of optimum rate of supply of added ammonia gas (partial pressure) is established in terms of the partial pressure relationship between the two materials: source-material gas (TDAAT) and added ammonia gas.
Specifically, a method according to this invention includes a method of manufacturing a titanium nitride thin film at the surface of a substrate by the chemical vapor deposition method (CVD method) by supplying tetrakisdialkylamino titanium (TDAAT) and ammonia into a reaction vessel, and heating it to a prescribed temperature under a low pressure of less than 100 Pa total pressure, wherein the partial pressure PTDAAT of the source-material gas (TDAAT) is set in a range of 0 less than PNH3/PTDAAT less than 10 with respect to the partial pressure PNH3, of the added ammonia gas, and wherein the tetrakisdialkylamino titanium (TDAAT) is tetrakisdiethylamino titanium (TDEAT).
Also, this invention relates to a device for manufacturing titanium nitride thin film, the device including a reaction vessel capable of vacuum pumping; a vacuum pumping device capable of maintaining the interior of the reaction vessel at low pressure of less than a total pressure of 100 Pa by evacuating the interior of this reaction vessel; a gas supply device for introducing source-material gas into the reaction vessel; a substrate holder that holds a substrate onto which the titanium nitride thin film is deposited; and a heating device that heats the substrate; characterized in that it comprises a mass flow controller and pressure controller such as to make the partial pressure PTDAAT of the source-material gas (TDAAT) satisfy the relationship 0 less than PNH3/PTDAAT less than 10 with respect to the partial pressure PNH3 of an added ammonia gas.
In general, the film growth species (precursor of formation of TiN film) of TDAAT source-material gas used on its own has a high probability of sticking and low diffusion speed with respect to the substrate surface.
Specifically, it may be predicted that within contact holes, as the aspect ratio (contact hole depth H/hole diameter D) becomes larger, most of the TDAAT film growth species, due to the properties of the TDAAT film growth species, will be immediately deposited on the inside wall in the vicinity of the concavity of the contact hole, resulting in little of the film growth species being able to diffuse in the depth direction, so producing poor step coverage.
However, due to the addition of ammonia gas, which is of a high diffusion coefficient, to the source-material TDAAT gas, the ammonia gas displays high reactivity with the TDAAT. The ammonia gas easily diffuses in the depth direction within the contact holes. As a result, a supply of film growth species thereto is increased, resulting in the benefit that TiN film is formed uniformly on the side walls in the depth direction or at the bottom.
Furthermore, regarding the amount of this added ammonia, as mentioned above, it is desirable that a trace supplied amount should be set such that 0 less than PNH3/PTDAAT less than 10, where PTDAAT is the partial pressure of the source-material gas and PNH3 is the partial pressure of the ammonia gas.
In order to clarify the reasons for the control of the supplied amount, the relationship between coverage and the ratio (PNH3/PTDAAT) of the partial pressure of the ammonia with respect to the partial pressure of the TDAAT was investigated.
The substrate temperature was set within the range of 300xc2x0 C. to 350xc2x0 C., which is believed to constitute a practically useful typical temperature range.
From FIG. 3, it can be seen that, as the partial pressure of the ammonia increases with respect to the partial pressure of TDAAT, there exist a region (A) in which coverage changes abruptly, and a region (B) in which coverage is fixed without displaying any change. Also, the point (this will be called PCN) at which the coverage starts to cease to display change with respect to PNH3/PTDAAT shows a lower value in terms of PNH3/PTDAAT value at 350xc2x0 C. than it does at 300xc2x0 C. It may be predicted that PCN shifts to low values of PNH3/PTDAAT as the substrate temperature becomes higher than 300xc2x0 C.
From the above, it was established that, regarding the optimum amount of ammonia to be added, a prescribed amount of 0 less than PNH3/PTDAAT less than 10 in relation to the partial pressure of the source-material TDAAT is desirable. The device construction and process conditions used in reaching the results of FIG. 3 are described in detail in the preferred embodiments described herein.
The flow rates of the TDAAT and ammonia gas can be adjusted by respective mass flow controllers. The TDAAT and ammonia gas flow rates relative to the respective carrier gas N2 can also be adjusted by dedicated mass flow controllers.
TDEAT may be employed as the TDAAT. The carrier gas does not contribute to the chemical reaction with TDAAT, and it is appropriate to employ nitrogen gas in both cases.